The present invention relates to a process for treating an exhaust gas containing substantially only ammonia gas and oxygen as reactive components by contacting the exhaust gas with a specific catalyst which exhibits an activity for decomposition of ammonia at an elevated temperature.
An exhaust gas from, such as, an ammonia production plant, a copying machine using ammonia sensitive paper, a plant for removing nitrogen oxides in which ammonia gas is added to an exhaust gas from a boiler or nitric acid production plant, or the like, contains ammonia gas and oxygen. The ammonia gas contained in the exhaust gas can be a cause of air pollution. In the nitrogen oxide removing plant in which an excess amount of ammonia gas relative to an amount of nitrogen oxides in the exhaust gas is added to prevent completely leak of the nitrogen oxides in the exhaust gas from the plant. As a result, a small amount of ammonia gas is contained in a treated exhaust gas while no nitrogen oxide is contained therein. The leak of ammonia gas is not only a cause of air pollution, but also a cause of clogging of tubing of the plant because the ammonia gas reacts with acidic gases, such as SO.sub.3, in the exhaust gas thereby forming ammonium salts.
As ammonia gas is easily absorbed in water, the ammonia gas has conventionally been removed by a liquid absorption method. However, this method may bring about a new problem because there is a necessity to treat the liquid that has absorbed the ammonia gas.
Accordingly, decomposition of ammonia gas to nitrogen and water is much better than the liquid absorption method. Heretofore, in a process for treating ammonia gas so as to oxidize the ammonia gas to nitrogen monoxide, platinum group catalysts or platinumrhodium series catalysts have been used at a temperature higher than 800.degree. C. This process has a serious problem that the reaction product, i.e. nitrogen oxide, is harmful to human beings. The high reaction temperature of this process is not suitable for treating an exhaust gas because the exhaust gas to be treated must generally be heated up to such high temperature.
There have been known various catalysts for oxidizing ammonia which comprise, such as, oxides of cobalt, nickel, copper, bismuth and/or manganese. In this process using the oxides, nitrogen monoxide and nitrogen oxides are formed. Moreover, this process is difficult to effect at low temperatures of such as 300.degree. to 400.degree. C because of a low activity of the catalysts.